The present invention relates to a method for the overlapping welding of sheet-like plastic materials by means of a heating wedge which is moved between the upper and the lower web and heats the materials, the material webs, after heating and fusing, being combined and being pressed together. The invention relates, moreover, to a welding appliance for the overlapping welding of sheet-like plastic materials, with a carriage carried and driven by rollers, at least one of the rollers being designed as a pressure roller for pressing together the materials brought, hot, into contact with one another, and a heating device which can be introduced between the material webs and which, during contacting, fuses the material webs on the sides facing one another, and to the use of a guide rail for welding appliances of this type.
For the welding of sheetings consisting of coated fabric, films and sealing webs made from PVC-P, PE, ECB, CSPE, EPDM, PVDF etc. and also PE-coated list fabrics for motor trucks, tents, coverings in agriculture, biotopes, swimming pools, awnings, boat tarpaulins, inflatable boats, publicity sheetings, etc., the method initially described is employed and welding appliances of this type are used. Further similar materials occur in civil engineering, roof building or floors. The above-described plastic materials are designated below, in general, as material webs. For welding, the material webs are arranged in an overlapping manner, so that, in an overlapping region, the two material webs lie one on the other and are designated as an upper material web and a lower material web. It is also possible for the material webs to be welded together to be butted and for a strip, which covers both lower layers in an overlapping region, to be welded to the in each case lower material web.
The welding appliances may in this case have as a heating device a heating wedge, which is normally electrically heated directly, or a heating nozzle, which is to be arranged between the materials and is heated by hot air. Particularly with regard to the heating-wedge welding appliances and to the methods employed in this case, it is necessary to lift the materials to be welded, in order, after welding, to press together the material webs with sufficient force by means of pressure rollers on both sides of the materials to be welded. Examples of this machine type and of the method employed in this case may be gathered from DE 42 30 882 C2 or U.S. Pat. No. 5,865,942 A1. This method and the welding appliances used for the purpose have the disadvantages that, by the material webs being lifted, on the one hand, they may form creases which impair the weld seam, and, furthermore, there is the risk of distortion of the material webs. Furthermore, the handling of the welding appliance is made more difficult by the sometimes relatively thick and rigid material webs when these material webs are being lifted.
The object of the present invention is to provide a method and an apparatus by means of which the welding of material webs is improved and handling is facilitated.